Earth Minerals
Minerals
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Crystalline solid
Pure substance
Found in nature
Inorganic
Rocks
• Solid aggregate of
minerals (mixtures)
Physical Properties
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Color
Luster
Cleavage
Hardness
Streak
Crystal Form
Specific Gravity
Special Properties
Color
• Most obvious characteristic of minerals
• Most unreliable characteristic for
identifying minerals
• Impurities cause color variations
• Example: Quartz
Luster
• Appearance or quality of light reflected
from the surface of the mineral
• Descriptions:
Metallic – look like metal regardless of
color
Cleavage
• A minerals tendency to break along flat
surfaces
– Depends on the type of bond used during
the formation of mineral
• Fracture – minerals that break unevenly
into curved or irregular pieces
• How to test: break the mineral
Hardness
• Measure of minerals ability to resist
scratching
• Does not mean resistance to cleavage or
fracture
• Hardest mineral – diamond
• Hardest common mineral – quartz
• Softest common mineral - talc
• How to test – rub mineral along a glass slide
to see if it scratches the glass or not
Streak
• Color of a mineral in its powdered form
• More reliable indication of mineral color
• How to test: rub mineral against streak
plate
Crystal Form
• External
expression of a
mineral’s internal
orderly
arrangement of
atoms
• How crystals will
grow without
interference
Specific Gravity
• How dense a mineral is compared to
water
• Minerals denser than water have a
density greater than 1
– Quartz, feldspar, calcite, and talc – 3
specific gravity
– Hematite and magnetite – 5 specific gravity
– Gold – specific gravity – 19.3 when pure
• Minerals less dense than water have a
density below 1
Specific gravity…
Specific gravity =
weight of sample in air
loss of weight in water
Special Properties
• Magnetic –
– Magnetite – most common magnetic mineral
– Lodestone – type of magnetite that acts
like a magnet
• Fizzes with acid:
– Calcite will fizz when hydrochloric acid is
placed on the sample
– The fizz produces carbon dioxide gas CO2
• Taste:
– Mineral will have a particular taste like salt
– How do you test – lick it
• Fluorescence
– Minerals absorb ultraviolet light and then
produce visible light of various colors
– Calcite appears white but under UV light
appears red
• Odor –
– Minerals that
smell
– Sphalerite – rich
in zinc
– How to test –
scratch the
mineral and smell
• Double Refraction –
– Light rays that bend as they pass through
the mineral
– When the light bends it splits into 2 rays
and produces a double image
Mineral ID practice…
What is…?
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How Crystalline Minerals Form
• Evaporation of solutions
– Halite and Gypsum
• Cooling of melted substances
– Quartz and Olivine